FR2615564A1 - METHOD FOR ARRANGING, IN A COMBUSTION CHAMBER OF A TWO-STROKE ENGINE, A FUEL SUPPLY SYSTEM RELATING TO THE EXHAUST LIGHT AND MOTOR THUS DESIGNED - Google Patents

Abstract

The invention relates to a two-stroke internal combustion engine having at least one combustion chamber fitted with a delayed fuel feed system (8) opening out into a cylinder head (1), the wall of the cylinder comprising at least one exhaust port (10) located next to a first reference point (10a) through which passes a first axial plane of the cylinder or exhaust plane and at least one admission port (11) located next to a second reference point (11a), or admission reference point. This engine is characterised in that the plane perpendicular to the exhaust plane and containing the axis (P) of the cylinder (2) defines two cylinder control zones in which the first (4a) complementary to the second (4b) contains the reference point (10a) for the exhaust port and in that the feed system is located in the second control zone (4b).

Description

The present invention relates to an arrangement of the various organs

  inside a combustion chamber a two-stroke engine to

internal combustion.

  More particularly, the invention relates to two-stroke engine combustion chambers having intake and exhaust ports and a deferred fuel feed system.

at the level of the breech.

  The two-stroke engine combustion study revealed the importance of combustion initiation conditions for obtaining

  correct and complete combustion of the fuel introduced.

  This initiation of combustion depends essentially on the internal aerodynamics and the conditions prevailing in the vicinity of the ignition point, particularly with regard to the richness of the mixture.

near this point.

  The complete combustion of the fuel introduced depends in particular on the quantity of fuel introduced remaining in the combustion chamber.

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  In fact, in the engines where the fuel is introduced before the exhaust port is closed off, a certain portion of the fuel may end up in the exhaust without burning in the combustion chamber.

  This results in consumption and significant pollution of the engine.

  This boredom is particularly increased in Engines admitting to

  Carbide air for flue gas scavenging.

  Also, the use of a non-carbureted fresh air intake ensuring flue gas scavenging, combined with a delayed fuel supply system triggered once fresh air is introduced into the chamber, would be able to prevent the exhaust of unburned fuel, if it were not essential for combustion (in particular as regards the homogenisation of the fuel mixture in the fresh air), to introduce the fuel before the exhaust is exhausted

  closes, with the risk that some of the fuel escapes.

  The deferred fuel supply system may comprise either an injector opening directly or indirectly into the combustion chamber and controlled for example electronically or by cam depending on the rotation of the crankshaft, or an injector

  pneumatic, as described in FR-A-2,575,521.

  In a two-stroke engine comprising a pneumatic injector placed in the cylinder head, the respective positions of the pneumatic injector and the ignition point in the combustion chamber represent important parameters of the internal aerodynamics and therefore of the

  conditions for initiation of combustion.

  Mainly in order to reduce unburnt and improve the conditions for initiation of combustion, and therefore of combustion, the present invention proposes different arrangements of the combustion chamber.

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  -3- combustion. The arrangements developed according to the invention could be studied theoretically and experimentally, in particular by means of numerical simulation and engine tests. For two-stroke engines equipped with a pneumatic fuel injector in the cylinder head, the arrangements designed and selected for their interest are characterized in that the ignition point is placed on the exhaust side, or that the injector pneumatic is placed on the opposite side of the exhaust, or also that the pneumatic fuel injector is installed on the side of the intake lights

  rear, such as rear transfer lights.

  Fortunately for the manufacture of engines, these conditions

  are compatible with a simple engine architecture.

  Thus, the present invention relates to a two-stroke internal combustion engine having at least one combustion chamber equipped with a deferred fuel feed system opening into a cylinder head which covers a cylinder cooperating with a piston, the cylinder head, the cylinder and the piston defining the combustion chamber, the wall of the cylinder comprising at least one exhaust port located in the vicinity of a first reference point through which passes a first axial plane of the cylinder or exhaust plane and at least one light intake located in the vicinity of a second reference point, or

  reference point of admission.

  It is characterized in that the plane perpendicular to the exhaust plane and containing the axis of the cylinder defines two cylinder development zones, the first complementary to the second contains the reference point of the exhaust port and that the feeding system is located in the second planning area. - 4 - The cylinder head may include a spark plug which may be

  located in the first planning area.

  The reference point of admission may be in the second zone. The feed system may be adapted to produce a convergent jet in the second layout zone and substantially oriented

  towards the reference point of admission.

  The feed system can be adapted to produce a divergent jet which on the one hand passes through said second zone of development and is oriented towards the reference point of the intake and which on the other hand is directed towards the first zone of development

neighborhood of the breech.

  The supply system may be a pneumatic injection system and it may include a deflector adapted to

change the shape of the jet.

  The feeding system can be adapted to produce a jet

  diverging in said perpendicular plane.

  The feed system may be adapted to produce a jet oriented substantially counter-current of the loop (s) of gas scanning. In addition, the present invention relates to a method for designing an internal combustion two-stroke engine having at least one combustion chamber equipped with a delayed fuel supply system, the chamber being delimited by a cylinder head, a cylinder and a piston, the wall of the cylinder having at least one exhaust port located in the vicinity of a first reference point and at least one intake port located in the vicinity of a second

  reference point, or reference point of admission.

  This method is characterized in that the arrangement and shapes of at least one intake port are adapted to produce a stream of fresh gas initially substantially directed to the feed system, and in that the supply system is placed as close as possible to the reference point of the

  admission, following the flow of fresh gas.

  The invention can be well understood and all its advantages

  will become clear from reading the following description,

  illustrated in the appended figures in which: - Figure 1 shows schematically in section the arrangement of a motor according to the prior art, - Figure 2 illustrates schematically in section a mode of arrangement of an engine according to the invention, FIGS. 3A to 3F show, during the movement of the piston, the fuel isoconcentrations obtained by a numerical simulation for the arrangement of an engine according to the prior art illustrated by FIG. 1; FIGS. 4A to 4F represent during the movement of the piston, the fuel isoconcentrations obtained by a numerical simulation for the mode of arrangement of an engine according to the invention illustrated in FIG. 2; FIG. 5 schematizes in section a second mode of arrangement; of an engine according to the invention using a divergent baffle, r - Figure 6 schematizes in section a third mode of arrangement of an engine according to the invention using a convergent baffle, and - 7 - - Figure 7 illustrates schematic ematically in section through a plane perpendicular to the sectional plane of FIGS. 1, 2, 5 and 6, a mode of arrangement of an engine according to the invention using a deflector

  diverge in this perpendicular plane.

  In FIG. 1, which schematically represents the arrangement of an engine according to the prior art, reference numeral 1 denotes the cylinder head closing the upper part of the cylinder 2 inside which

  moves a piston 3 connected by a connecting rod 6 to a crankshaft 7.

  The combustion chamber has the reference 4 and the lower case

the reference-5.

  The cylinder head 1 comprises a spark plug 9 creating an ignition point by an electric arc and a deferred fuel supply system 8

  which can be a pneumatic injection system.

  The exhaust manifold communicates with the cylinder 2 by a

light 10.

  The intake manifold communicates with the cylinder 2 by a rear light-11 and by one or more side lights 12. All these

  lights may have one or more orifices.

  The cylinder 2, like the sliding piston 3, is assumed to revolve around a P axis as in practice. It will not be beyond the scope of the invention using cylinder shapes and piston

  significantly different from those of revolution.

  If it is considered that the exhaust port 10 is located around a first reference point 10a, and that the exhaust plane contains this point and the axis of the cylinder, the plane perpendicular to the exhaust plane and passing through the axis of the cylinder delimits in the combustion chamber two distinct zones of development, the first of which 4a complementary to the second 4b contains the point of

  reference 10a of the exhaust port.

  According to the prior art (FIG 1) the fuel supply system 8 is located in the first zone 4a of arrangement, that is to say on the same side as the reference point 10a of the light

  exhaust 10 relative to the perpendicular plane.

  Similarly, the second reference point 11a, or reference point of admission, around which the rear inlet 11 and side 12 are located, is located in the second layout area 4b with the candle 9, then that the power system

  8 is located in the first planning area 4a.

  According to the invention (FIG 2), the reference point 11a of the intake as the fuel supply system 8 is located in the second zone of development, that is to say on the opposite side to the point reference 10a of the exhaust light, relative to the perpendicular plane whose line P is the front trace on the plane of the figure. Finally, the candle 9 is located in the first zone

4a.

  The positions of the intake and exhaust ports are respectively from a first and a second

  reference point around which the lights are located.

  The reference points correspond substantially to the application points of the vectorial results of the gas velocities at

  level of intake and exhaust lights.

  However, since obtaining the results is difficult, it can often be considered that the reference point corresponds to the barycentre of the surfaces of the lights on the one hand intake and on the other hand exhaust. Thus, when an exhaust system has two lights, the reference point of the exhaust is between the two lights or the lights are located around said reference point of the exhaust. Figures 3A to 3F and 4A to 4F illustrate the fuel concentration changes occurring in a combustion chamber during crankshaft rotation. These figures were obtained by a two-dimensional modeling of a combustion chamber taking into account the interaction of the scanning loop formed by the mass of fresh gas admitted by the intake light,

  with the jet of the pneumatic injector.

  The straight segment 14 greater than the figures illustrate the cylinder head while the locus 15 corresponds to the fuel supply zone. The straight vertical segments 16 represent the walls of the cylinder and the

  lower right segment 17 represents the piston.

  In order for the modeling to reproduce as accurately as possible the behavior of the gases inside the combustion chamber, particularly with regard to the scanning, it is considered that the admission is effected by two lights symbolized by the zones 19a and 19b 'and that the escape is effected by a light symbolized by

zone 18.

  The intake ports open at 55o before the bottom dead center and close 55 after the bottom dead center (respectively 125 and 235 respectively).

crankshaft angle).

  The exhaust port opens at 71 before the bottom dead center and closes at 71 after the bottom dead center (respectively 109 and 251).

crankshaft angle).

  A first inlet lumen 19a introducing air at an initial angle of zero degrees to the horizontal is placed in front of a second inlet lumen 19b introducing air under

  an initial angle of 60 degrees to the horizontal.

  The exhaust port 18 is placed above the first

admission light 19a.

  Since the fuel concentration is the mass of fuel relative to the mass of the mixture of fresh air, flue gas and fuel, the isoconcentration lines delimit ranges of wealth including references corresponding to the following values of the fuel concentration: Reference of the zone Fuel concentration range R1 less than 0.01 R2 between 0.01 and 0.02 R3 between 0.02 - and 0.03 R4 between 0.03 and 0.05 R5 between 0.05 and 0.075 R6 more than 0.075 FIGS. 3A to 3F illustrate the modeling of a chamber of

  substantially in accordance with that of Figure 1.

  The different figures were produced for different angles of the crankshaft corresponding to the following indications: Figure Angle crankshaft

3A 213

3B 2350

3C 251

3D 277

3E 303

3F 330

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  For these figures (3A to 3F), the feed system includes a deflector for giving an initial direction to the jet inclined 20 relative to the axis of the cylinder to the rear intake port. The modeling of FIGS. 3A to 3F shows that the jet retains its initial direction for a very short time and that, very quickly, it is deflected towards the exhaust by the scanning loop which is driven by a substantially gyratory movement in the clockwise direction. the plan of

FIGS.

  FIG. 3F, which shows the isoconcentrations in the chamber when the crankshaft angle is 330 (that is at the moment when the ignition occurs), shows that the interaction of the air jet with the scanning loop has generated a richer fuel zone on the exhaust side o is also the pneumatic injector. But alas, however, the candle for architectural considerations difficult to respect can not be on the rich side and is placed on the opposite side. This result perfectly illustrates the experimental observations made on a similar configuration engine that becomes unstable, especially at high speed. This event confirms everything

  in fact bad conditions of combustion.

  As FIG. 3C represents the chamber at the time of closing of the exhaust port, it is possible to understand, with the aid of the

  Figure 3B that a portion of the fuel goes directly to the exhaust.

  The modeling calculations make it possible to estimate at 8% of the losses by

  imbrOlés for the engine configuration studied.

  FIGS. 4A to 4F illustrate the modeling of a combustion chamber according to the invention substantially in accordance with that of FIG. 2 and in which the supply system comprises a

2 6 1 5 5 6 4

- i1 -

  deflector for giving an initial direction to the inclined jet

  of 20 relative to the axis of the cylinder to the exhaust port.

  The different figures were produced for different crank angles corresponding to the following indications: Figure Crankshaft angle

4A 211

4B 235

4C 251

4D 271

4E 310

4F 330

  Thanks to the modeling shown in FIGS. 4A to 4F, it is observed, as before, that the fuel jet keeps very little time in its initial direction and that it is deflected towards the exhaust by the loop.

  circulating sweep as in the earlier engines.

  The various figures show that with the configuration according to the invention, the rich zones take longer to reach the exhaust due to the length of the path to be traveled between the fuel system and the exhaust, that they 'spread better across the chamber and that finally the gaseous mixture is usually more

  uniform when ignition occurs (Fig. 4F).

  Modeling calculations allow for this configuration of

  engine to evaluate at 4% the losses by unburnt.

  In addition, the candle placed on the exhaust side is located in a rather richer area o can be an excellent initiation of combustion. This result is confirmed experimentally on the engine where we achieve high operating speeds without

  particular manifestation of instability of combustion.

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  Figures 5, 6 and 7 show the importance of jet direction

  initials from the power system 8.

  In these embodiments, a pneumatic injector 8 such as that described in patent FR-A-2,575,522 is used. A member 20 injects fuel into the nozzle 23 placed in a stream of compressed air. An injection valve 22 resting on a seat 24 isolates the injection system 8 from the chamber

  2 when the compression pressure has reached a certain threshold.

  The system includes deflectors 25, 26, 27 integrated into the seat

  allowing to modify the initial incidence of the jet.

  The deflectors make it possible to create very favorable conditions for the initiation of combustion and to slow down the path of the pneumatic jet of fuel towards the exhaust port, in order to

  reduce the amount of unburned fuel.

  Thus, in FIG. 5, a diverging deflector 26 is used, slowing the penetration of the pneumatic jet. Part of this jet 26a is directed towards the face of the cylinder closest to the injector 8 in order to reduce, by opposing, the drive of the scanning loop.

  Figure 6 illustrates an engine with a counter deflector

  current, on the one hand to increase the path followed by the scanning loop to avoid losses of unburned exhaust and on the other hand, to keep part of the jet along

  the wall of the cylinder closest to the injection system.

  FIG. 7 schematizes a combustion chamber comprising a deflector 27 diverging along a plane parallel to said perpendicular plane. This provision allows to slow down, in this plan

2 6 1 5 5 6 4

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  parallel to said perpendicular plane, the penetration of the pneumatic jet of fuel so as to reduce the losses by imbrigles.

96 15564

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Claims (10)

R E V E N D I C A T.I O N S   1. - Two-stroke internal combustion engine having at least one combustion chamber equipped with a deferred fuel supply system (8) opening into a cylinder head (1) which covers a cylinder (2) cooperating with a piston ( 3), the cylinder head, the cylinder and the piston defining said combustion chamber (4), the wall of the cylinder comprising at least one exhaust port (10) located in the vicinity of a first reference point (10a) through which passes a first axial plane of the cylinder or exhaust plane and at least one intake port (11) located in the vicinity of a second reference point (1a), or reference point of the intake, which engine is characterized in that the plane perpendicular to the exhaust plane and containing the axis (P) of the cylinder delimits two zones of arrangement of the cylinder, the first (4a) complementary to the second (4b) contains the reference point (10a) of the exhaust light and in that the feeding system is located in said second (4b) planning area.   2. - Engine according to claim 1, characterized in that said cylinder head comprises a spark plug (9) and in that said candle   is located in said first planning area (4a).   3. - Motor according to one of claims 1 and 2, characterized in that   that the reference point of admission (11a) is located in the second zone (4b).   4. -Engine according to one of claims 1 to 3, characterized in that   the feeding system (8) is adapted to produce a convergent jet (25a) (Fig. 6) in said second accommodation zone and substantially oriented towards said admission reference point; (11a). - 15 -   5. - Motor according to one of claims 1 to 3, characterized in that   that the feed system (8) is adapted to produce a divergent jet (26a) which passes through said second zone (4b) of arrangement and is oriented towards the reference point (11la) of the intake and which is directed towards said first planning area in the vicinity of the cylinder head (1).   6. - Engine according to one of claims 1 to 5, characterized in that   that said feeding system (8) is an injection system pneumatic.   7. - Engine according to claim 6, characterized in that said pneumatic injection system (8) producing a jet of fuel gas comprises a valve (22) and a suitable baffle (25, 26, 27) to modify the shape of said jet.   8. - Motor according to one of claims 1 to 7, characterized in that   that the feeding system is adapted to produce a divergent jet   in said perpendicular plane (Fig. 7).   9. - Engine according to one of claims 1 to 7, characterized in that   that the feed system is adapted to produce a jet oriented substantially countercurrently to the gas sampling loop (s). 10. - Method for designing an internal combustion two-stroke engine having at least one combustion chamber equipped with a delayed fuel supply system (8), said chamber being delimited by a cylinder head (1), a cylinder (2) and a piston (3), the wall of the cylinder including at least one exhaust port (10) located in the vicinity of a first reference point (10a) and at least one intake port (11) located in the vicinity of a second reference point (11a), or reference point of admission, this method is characterized in that the arrangement and the - 16 -   forms of at least one intake light so as to produce a fresh gas stream initially sensibly directed towards the supply system, and that the supply system is placed as close as possible to the reference point. of admission, following the flow of fresh gas.